1. Field of the Invention
This invention generally relates to an imaging apparatus and particularly to an electrostatic imaging apparatus for forming an image on a photosensitive member according to an electrophotographic image forming process.
2. Description of the Prior Art
A transfer type electrophotographic copying apparatus is well known in the art. In such an apparatus, use is made of a photosensitive member which is first uniformly charged to a predetermined polarity by means of a corona discharger and then exposed to a light image thereby causing the uniform charge to be dissipated selectively thereby forming an electrostatic latent image, followed by the steps of developing the latent image to convert the latent image into a visible toner image and transferring the toner image to a transfer medium, such as plain paper. In a repetitive process as in a commercial apparatus, the photosensitive member is typically cleaned prior to the next sequence of operation. FIG. 1 shows a typical prior art corona discharger 1 for use in charging the surface of a photosensitive member 3 uniformly. The prior art corona discharger 1 is normally provided with grid electrodes 2 in an integrated structure and provided as detachably mounted in position close to the photosensitive member 3.
As described above, there remains residual toner on the photosensitive member 3 after transfer. Thus, there is normally provided a cleaning device for cleaning the photosensitive member 3 after transfer. Even so, a slight amount of toner may still remain on the photosensitive member 3 and it may be attracted to the grid electrodes 2 located close to the photosensitive member 3 so that the grid electrodes 2 become contaminated. Furthermore, some of such residual toner may also be attracted to a corona wire 1a passing through the grid electrodes 2, and when the corona wire 1a becomes contaminated due to such deposition of toner, its discharging characteristic could be severely impaired.
Thus, it is often required to clean the corona wire 1a. However, with the prior art structure as shown in FIG. 1, since the grid electrodes 2 are integrally formed with the corona discharger 1 thereby having the corona wire 1a enclosed, it is difficult to clean the corona wire 1a. Moreover, after using for a substantial period of time, the grid electrodes 2 also come to be required to be cleaned. However, since the grid electrodes are typically comprised of a plurality of wire elements having the diameter in the order of 0.1-0.2 mm and arranged in a relatively complicated pattern, cleaning of such grid electrodes is rather difficult and time consuming.